This invention relates to a package for some of the ingredients (additives) to be added to a polymer formulation, to packages containing additives for polymer formulations, and to a method of compounding polymer formulations using said packages. More particularly, the invention relates to packages for additives to be added to polymer formulations where the formulation contains at least one component which is a solvent for the package.
This invention relates generally to the compounding of any polymer formulation containing at least one component which is a solvent for the polystyrene package described below. The invention particularly is suitable for compounding polyester resin, vinyl resin or rubber formulations to which are added materials which modify the physical and/or chemical properties of the formulation or of the cured product. The term "additive" is used in this specification and claims to embrace any such materials which are added to the polymer formulations. Exemplary additives include catalysts, colorants, antioxidants, ultraviolet stabilizers, fillers, reinforcements, thixotropic agents, inhibitors, mold release agents, flame retardants, plasticizes, fungicides, biocides, silanes to improve adhesion of the product to substrates or reinforcing fibers, etc.
The compounding of polymers generally requires the maintenance of quantities of a variety of additives to be introduced into the resin batches in rather precise amounts. The potential for error in the selection of the particular additives and in the measurement of the amounts of each additive each time portions of additives must be taken from bulk reservoirs and introduced into the formulation is significant. Moreover, additives with short shelf lives may deteriorate before they can be used.
Some additives consist of suspensions of particles in liquid vehicles, and the particles may tend to settle out on standing. For example, sensitive catalysts such as the organic peroxides and azo compounds used in compounding polyester resin formulations are suspended in inert liquid vehicles, and, consequently, when a selected amount of suspension is removed from a bulk container, the actual concentration of the particles may vary depending on the amount of settling which has occurred.
Various approaches have been suggested in the prior art for solving the foregoing problems. One approach involves the packaging of the additives in a thin wall sealed additive package which is soluble in the resin formulation. In U.S. Pat. No. 3,784,005, I disclosed a novel and improved soluble additive package which comprised a packaged envelop consisting of a thin film of polystyrene or other polymer film which was soluble in the resin formulation. The package envelope was made of extremely thin film, preferably not more than about five mils in thickness and more preferably not more than about two mils in thickness. This envelope is readily soluble in the resin formulation. Because of its thickness, the envelope is formed within and supported by a rigid outer container. In use, the envelope is removed from the rigid container and deposited directly into the resin formulation batch. The method of forming such packages for additives is described in my earlier U.S. Pat. No. 3,896,600.
U.S. Pat. No. 3,902,596 also describes additives packages of the type described in U.S. Pat. No. 3,784,005, but which differ in the nature of the stabilizing vehicle utilized to suspend the sensitive catalyst. In this patent, the vehicle is described as being selected from the group consisting of castor oil, menhaden oil, coconut oil, cottonseed oil, soybean oil, peanut oil, linseed oil and fully saturated polyester resin.
Because some of the polymerization initiator catalysts such as the organic peroxide catalyst and organic azo catalyst are explosively decomposable upon being subject to shock, heat, friction or contamination with a reactive substance resulting in the formation of gaseous reaction products at an explosive rate, it is desirable and necessary to suspend the catalyst in liquid stabilizing vehicles as more fully described below. For example, benzoyl peroxide and organic azo catalysts such as, for example, 2,2-azo(bis-isobutylnitrile) are potentially explosively decomposable polymerization initiator catalyst, and these generally are handled as mixtures of up to about 60% by weight of catalyst suspended in inert stabilizing vehicle such as a phthalate ester which substantially reduces the explosion hazard posed by the catalyst. However, some of the conventional liquid stabilizing vehicles for sensitive catalysts rapidly attack and destroy the thin film of the package envelope used in the additive packages described above.
For example, in British Pat. No. 955,079, there is described a technique for suspending peroxide catalyst particles in a vehicle such as tricresyl phosphate, butyl phthalate or dioctylphthalate. While such materials serve as vehicles for sensitive catalysts and effectively eliminate the dangers of explosion, these materials attack polystyrene and other polymer films thereby precluding the use of thin polystyrene film additive packages for such sensitive catalyst and their stabilizing vehicles when reasonable shelf life is required. When longer shelf life is required, the catalysts must be suspended in a vehicle which will not attack polystyrene and other films used to form the additive package.
Although the additive packages utilizing the thin-walled plastic envelope described in my earlier U.S. Pat. Nos. 3,784,005; 3,896,600 and 3,902,596 have been successfully used as packages for sensitive catalysts, such additive packages do require the somewhat tedious preparation of the thin-walled plastic envelope within the rigid container, and, moreover, after the plastic envelope has been removed from the rigid container and introduced into a resin formulation, the rigid container must be discarded, or if reusable, returned to the manufacturer. Accordingly, the use of a rigid container in accordance with the prior art is a factor in the cost of the additive package, and because it must either be discarded or returned, presents a burdensome task for the user.
Although U.S. Pat. Nos. 3,784,005 and 3,896,600 suggest the possibility of using a rigid all polystyrene foam container, such containers have not, to my knowledge, been used commercially because the stabilizing vehicles used to suspend the catalyst exhibit strong tendencies to penetrate into the walls of the polystyrene foam container. Such penetration or "wicking" by capillary action is an undesirable occurrence.